650 THE ANCIENT LAKES OF WESTERN AMERICA: 
of the Great Basin have been completely dried up by evap- 
oration, and now their places are marked by alkaline plains 
r "salt flats.” Others exist as lakes only during a portion 
of the year, and in the dry season are represented by sheets 
of glittering salt. Even those that remain as lakes are 
necessarily salt, as they are but great evaporating pans where 
the drainage from the. mountains — which always contains a 
portion of saline matter—is concentrated by the sun and 
wind until it becomes a saturated solution and deposits its 
surplus salts upon the bottom. 
The southern portion of the great central table land — that 
which has been denominated the Colorado Plateau—is al- 
most without mountain barriers or local basins, and we, 
therefore, find upon it fewer traces of ancient lakes, though 
they are not entirely wanting. It is apparent, however, that 
this high plateau, which stretches away for several hundred 
miles west of the Rocky Mountains, was once a beautiful 
and fertile district. The Colorado draining then, as now, 
the western ranges of the Rocky Mountains, spread over the 
surface of this plateau, enriching and vivifying all parts of 
it. When it reached the western margin of the table land, 
however, it poured over a’ precipice or slope five thousand 
feet in height, into the Gulf of California, which then 
reached several hundred miles farther north than now. In 
process of time the power developed by this stupendous 
fall cut away the rock beneath the flowing water, and formed 
that remarkable gorge to which I have already referred. 
This gorge is nearly one thousand miles in length and from 
three thousand to six thousand feet in depth, and is cut 
through all the series of sedimentary rocks from the Tertiary 
to the granite, and has worn out the granite to a depth of 
from six hundred to eight hundred feet. Just in proportion 
as the Colorado deepened its channel, the region bordering 
it became more dry, until ultimately the drainage from the 
mountains passed through it in what may be even termed 
und channels," and contributed almost nothing 
